Three terminal magnetic sensor having an in-stack longitudinal biasing layer structure in the collector region and a pinned layer structure in the emitter region

ABSTRACT

In one illustrative example, a three terminal magnetic sensor (TTM) suitable for use in a magnetic head has a sensor stack structure which includes a base region, a collector region, and an emitter region. A first barrier layer separates the emitter region from the base region, and a second barrier layer separates the collector region from the base region. A plurality of terminals of the TTM include a base lead coupled to the base region, a collector lead coupled to the collector region, and an emitter lead coupled to the emitter region. Preferably, the base region consists of a free layer structure so as to have a relatively small thickness. A pinned layer structure is made part of the emitter region. An in-stack longitudinal biasing layer (LBL) structure is formed in stack with the sensor stack structure and has a magnetic moment that is parallel to a sensing plane of the TTM for magnetically biasing the free layer structure. The in-stack LBL structure is made part of the collector region which also includes a layer of semiconductor material. In one variation, the emitter region has the in-stack LBL structure and the collector region has the pinned layer structure. The TTM may comprise a spin valve transistor (SVT), a magnetic tunnel transistor (MTT), or a double junction structure.

BACKGROUND

1. Field of the Technology

This invention relates generally to three terminal magnetic sensors(TTMs) suitable for use in magnetic heads, which includes spin valvetransistors (SVTs), magnetic tunnel transistors (MTTs), or doublejunction structures.

2. Description of the Related Art

Magnetoresistive (MR) sensors have typically been used as read sensorsin hard disk drives. An MR sensor detects magnetic field signals throughthe resistance changes of a read element, fabricated of a magneticmaterial, as a function of the strength and direction of magnetic fluxbeing sensed by the read element. The conventional MR sensor, such asthat used as a MR read head for reading data in magnetic recording diskdrives, operates on the basis of the anisotropic magnetoresistive (AMR)effect of the bulk magnetic material, which is typically permalloy. Acomponent of the read element resistance varies as the square of thecosine of the angle between the magnetization direction in the readelement and the direction of sense current through the read element.Recorded data can be read from a magnetic medium, such as the disk in adisk drive, because the external field from the recorded magnetic medium(the signal field) causes a change in the direction of magnetization inthe read element, which causes a change in resistance of the readelement and a resulting change in the sensed current or voltage.

A three terminal magnetic sensor (TTM) of a magnetic head may comprise aspin valve transistor (SVT), for example, which is a vertical spininjection device having electrons injected over a barrier layer into afree layer. The electrons undergo spin-dependent scattering, and thosethat are only weakly scattered retain sufficient energy to traverse asecond barrier. The current over the second barrier is referred to asthe magneto-current. Conventional SVTs are constructed using atraditional three-terminal framework having an “emitter-base-collector”structure of a bipolar transistor. SVTs further include a spin valve(SV) on a metallic base region, whereby the collector current iscontrolled by the magnetic state of the base region using spin-dependentscattering. Although the TTM may involve an SVT where both barrierlayers are Schottky barriers, the TTM may alternatively incorporate amagnetic tunnel transistor (MTT) where one of the barrier layers is aSchottky barrier and the other barrier layer is a tunnel barrier, or adouble junction structure where both barrier layers are tunnel barriers.

Since it is advantageous to form a very thin base region for increasedareal recording densities, it has been identified that the base regionin the TTM will have a relatively large electrical resistance. Given anestimated trackwidth (TW) of approximately 50 nanometers (nm) for amagnetic head, for example, the electrical resistance of the base regionmay be much greater than 100Ω. Thus, as the sense current passes throughthe base region from the emitter lead to the base lead, the base regionmay be prone to failure or damage (e.g. it could “blow” like a fuse).Further, a relatively large resistance for the base region raises thenoise floor for the TTM, such that a much larger input signal would berequired for suitable operation.

Another important consideration is that the free layer should belongitudinally biased parallel to the sensing (or ABS) plane andparallel to the major planes of the thin film layers of the TTM, suchthat the free layer is magnetically stabilized. This has been typicallyaccomplished by first and second hard bias magnetic layers which areadjacent to first and second sides of the TTM. Unfortunately, themagnetic field through the free layer between the first and second sidesis not uniform since a portion of the magnetization is lost in a centralregion of the free layer to the shields. This is especially troublesomewhen the track width of the TTM may be in sub-micron dimensions. Endportions of the free layer which abut the hard bias layers may beover-biased and become very magnetically stiff in their response tofield signals from the moving media. The stiffened end portions can takeup a large portion of the total length of the TTM and can significantlyreduce the signal amplitude of the TTM.

Accordingly, there is a need to solve these problems so that TTMs may besuitable for use in magnetic heads and other devices.

SUMMARY

In one illustrative embodiment of the present application, a threeterminal magnetic sensor (TTM) suitable for use in a magnetic head has asensor stack structure which includes a base region, a collector region,and an emitter region. A first barrier layer separates the emitterregion from the base region, and a second barrier layer separates thecollector region from the base region. A plurality of terminals of theTTM include a base lead coupled to the base region, a collector leadcoupled to the collector region, and an emitter lead coupled to theemitter region. Preferably, the base region consists of a free layerstructure so as to have a relatively small thickness. A pinned layerstructure is made part of the emitter region. An in-stack longitudinalbiasing layer (LBL) structure is formed in stack with the sensor stackstructure and has a magnetic moment that is parallel to a sensing planeof the TTM for magnetically biasing the free layer structure. Thein-stack LBL structure is made part of the collector region which alsoincludes a layer of semiconductor material. In one variation, theemitter region has the in-stack LBL structure and the collector regionhas the pinned layer structure. The TTM may comprise a spin valvetransistor (SVT), a magnetic tunnel transistor (MTT), or a doublejunction structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become more apparentto those skilled in the art after considering the following detaileddescription in connection with the accompanying drawings.

FIG. 1 is a cross-sectional view of a disk drive which may embody amagnetic head having a three terminal magnetic sensor (TTM) comprising aspin valve transistor (SVT);

FIG. 2 is a top-down view of the disk drive of FIG. 1;

FIG. 3 is an illustration for general SVT operation;

FIG. 4 is a perspective view of a TTM having a metal layer formed so asto reduce the base resistance;

FIG. 5 is a perspective view of another TTM having an alternative metallayer formed so as to reduce the base resistance;

FIG. 6 is a perspective view of yet another TTM having an alternativemetal layer formed so as to reduce the emitter resistance;

FIG. 7A is a sensor plane (or ABS) view of one embodiment of a TTM whichincludes a base region having a free layer structure, a pinned layerstructure, and an in-stack longitudinal biasing layer (LBL) structurewhich magnetically biases the free layer structure;

FIG. 7B is a sensor plane (or ABS) view of one variation of theembodiment of FIG. 7A where the layers in the base region are inverted;

FIG. 7C is a sensor plane (or ABS) view of another variation of theembodiment of FIG. 7A, where the base region has the free layerstructure, the in-stack longitudinal biasing layer (LBL) structure, anda self-pinned layer structure;

FIG. 7D is a sensor plane (or ABS) view of a variation of the embodimentof FIG. 7C, where the base region has the free layer structure, theself-pinned layer structure, and the in-stack longitudinal biasing layer(LBL) structure which also has a self-pinned layer structure;

FIG. 8A is a sensor plane (or ABS) view of another embodiment of a TTM,the TTM including a base region having a free layer structure and apinned layer structure, and a collector region having an in-stack LBLstructure which magnetically biases the free layer structure;

FIG. 8B is a sensor plane (or ABS) view of one variation of theembodiment of FIG. 8A, where the layers of the base region and thein-stack LBL structure are inverted such that the base region has thefree layer structure and the pinned layer structure and the emitterregion has the in-stack LBL structure;

FIG. 8C is a sensor plane (or ABS) view of another variation of theembodiment of FIG. 8A, where the base region has the free layerstructure and a self-pinned layer structure and the collector region hasthe in-stack LBL structure;

FIG. 8D is a sensor plane (or ABS) view of a variation of the embodimentof FIG. 8C, where the base region has the free layer structure and theself-pinned layer structure and the collector region has the in-stackLBL structure which also includes a self-pinned layer structure;

FIG. 9A is a sensor plane (or ABS) view of yet another embodiment of aTTM, the TTM including a base region having a free layer structure, anemitter region having a pinned layer structure, and a collector regionhaving an in-stack LBL structure which magnetically biases the freelayer structure;

FIG. 9B is a sensor plane (or ABS) view of one variation of theembodiment of FIG. 9A, where the base region has the free layerstructure, the emitter region has the in-stack LBL structure, and thecollector region has the pinned layer structure;

FIG. 9C is a sensor plane (or ABS) view of another variation of theembodiment of FIG. 9A, where the base region has the free layerstructure, the emitter region has a self-pinned layer structure, and thecollector region has the in-stack LBL structure;

FIG. 9D is a sensor plane (or ABS) view of a variation of the embodimentof FIG. 9C, where the base region has the free layer structure, theemitter region has the self-pinned layer structure, and the collectorregion has the in-stack LBL structure which also includes a self-pinnedlayer structure;

FIG. 10 is a sensor plane (or ABS) view of a final embodiment of a TTMof the double tunnel junction type which includes a base region having afree layer structure, an emitter region having a pinned layer structure,and a collector region having an in-stack LBL structure whichmagnetically biases the free layer structure;

FIG. 11 is a sensor plane (or ABS) view of an antiparallel (AP) pinnedlayer structure for use in the TTMs of FIGS. 7-10; and

FIGS. 12A-21B are illustrations of a TTM being fabricated according to aparticular method, preferably in the order presented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one illustrative embodiment of the present application, a threeterminal magnetic sensor (TTM) suitable for use in a magnetic head has abase region, a collector region, and an emitter region. A first barrierlayer separates the emitter region from the base region, and a secondbarrier layer separates the collector region from the base region. Asensing plane is defined along sides of the base region, the collectorregion, and the emitter region. The base region consists of a free layerstructure so as to have a relatively small thickness. A pinned layerstructure is made part of the emitter region. An in-stack longitudinalbiasing layer (LBL) structure which magnetically biases the free layerstructure is made part of the collector region. In one variation, theemitter region has the in-stack LBL structure and the collector regionhas the pinned layer structure. The TTM may comprise a spin valvetransistor (SVT), a magnetic tunnel transistor (MTT), or a doublejunction structure.

The following description is the best embodiment presently contemplatedfor carrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.

FIG. 1 is a simplified block diagram of a conventional magneticrecording disk drive for use with a three terminal magnetic sensor (TTM)of a magnetic head. FIG. 2 is a top view of the disk drive of FIG. 1with the cover removed. Referring first to FIG. 1, there is illustratedin a sectional view a schematic of a conventional disk drive of the typeusing a TTM. The disk drive comprises a base 510 to which are secured adisk drive motor 512 and an actuator 514, and a cover 511. Base 510 andcover 511 provide a substantially sealed housing for the disk drive.Typically, there is a gasket 513 located between base 510 and cover 511and a small breather port (not shown) for equalizing pressure betweenthe interior of the disk drive and the outside environment. A magneticrecording disk 516 is connected to drive motor 512 by means of a hub 518to which it is attached for rotation by drive motor 512. A thinlubricant film 550 is maintained on the surface of disk 516. Aread/write head or transducer 525 is formed on the trailing end of acarrier, such as an air-bearing slider 520. Transducer 525 is aread/write head comprising an inductive write head portion and a readhead portion. Slider 520 is connected to actuator 514 by means of arigid arm 522 and a suspension 524. Suspension 524 provides a biasingforce which urges slider 520 onto the surface of the recording disk 516.During operation of the disk drive, drive motor 512 rotates disk 516 ata constant speed, and actuator 514, which is typically a linear orrotary voice coil motor (VCM), moves slider 520 generally radiallyacross the surface of disk 516 so that read/write head 525 may accessdifferent data tracks on disk 516.

FIG. 2 illustrates in better detail suspension 524 which provides aforce to slider 520 to urge it toward disk 516. Suspension 524 may be aconventional type of suspension, such as the well-known Watroussuspension, as described in U.S. Pat. No. 4,167,765. This type ofsuspension also provides a gimbaled attachment of the slider whichallows the slider to pitch and roll as it rides on the air bearingsurface. The data detected from disk 516 by transducer 525 is processedinto a data readback signal by signal amplification and processingcircuitry in an integrated circuit chip 515 located on arm 522. Thesignals from transducer 525 travel via a flex cable 517 to chip 515,which sends its output signals to the disk drive electronics (not shown)via cable 519.

FIG. 3 illustrates TTM operation associated with a spin valve transistor(SVT) 300 which has a semiconductor emitter region 302, a semiconductorcollector region 304, and a base region 306 which contains a spin valve(SV). The semiconductors and magnetic materials used in SVT 300 mayinclude an n-type silicon (Si) material for emitter 302 and collector304, and a Ni₈₀Fe₂₀/Au/Co spin valve for the region 306. Energybarriers, also referred to as Schottky barriers, are formed at thejunctions between the metal base 306 and the semiconductors. It isdesirable to obtain a high quality energy barrier at these junctionswith good rectifying behavior. Therefore, thin layers of materials (e.g.platinum and gold) are oftentimes used at the emitter 302 and collector304, respectively. Moreover, these thin layers separate the magneticlayers from the semiconductor materials.

A TTM operates when current is introduced between emitter region 302 andbase region 306, denoted as I_(E) in FIG. 3. This occurs when electronsare injected over the energy barrier and into base region 306 by biasingthe emitter such that the electrons are traveling perpendicular to thelayers of the spin valve. Because the electrons are injected over theenergy barrier, they enter base region 306 as non-equilibrium hotelectrons, whereby the hot-electron energy is typically in the range of0.5 and 1.0 eV depending upon the selection of the metal/semiconductorcombination. The energy and momentum distribution of the hot electronschange as the electrons move through base region 306 and are subjectedto inelastic and elastic scattering. As such, electrons are preventedfrom entering collector region 304 if their energy is insufficient toovercome the energy barrier at the collector side. Moreover, thehot-electron momentum must match with the available states in thecollector semiconductor to allow for the electrons to enter collectorregion 304. The collector current I_(C), which indicates the fraction ofelectrons collected in collector region 304, is dependent upon thescattering in base region 306 which is spin-dependent when base region306 contains magnetic materials. Furthermore, an external appliedmagnetic field controls the total scattering rate which may, forexample, change the relative magnetic alignment of the two ferromagneticlayers of the spin valve. The magnetocurrent (MC), which is the magneticresponse of the TTM, can be represented by the change in collectorcurrent normalized to the minimum value as provided by the followingformula: MC=[I^(P) _(C)−I^(AP) _(C)]/I^(AP) _(C) where P and AP indicatethe parallel and antiparallel state of the spin valve, respectively.

In FIG. 4, a three terminal magnetic sensor (TTM) 400 of the spin valvetransistor (SVT) type is shown. Although described as incorporating anSVT (where both barrier layers are Schottky barriers), the TTM mayalternatively incorporate a magnetic tunnel transistor (MTT) (where oneof the barrier layers is a Schottky barrier and the other barrier layeris a tunnel barrier), or a double junction structure (where both barrierlayers are tunnel barriers). TTM 400 of FIG. 4 has a base region 15, acollector region 20 which is adjacent base region 15, an emitter region5, and a barrier region 10 which separates emitter region 5 from baseregion 15. As described in relation to FIG. 3, collector region 20 maybe a semiconductor substrate made of silicon (Si). Base region 15preferably includes at least one soft ferromagnetic (FM) material, suchas nickel-iron (NiFe), cobalt-iron (CoFe), or cobalt (Co), as well as avery thin metal (e.g. gold) which is sandwiched in between the FMmaterials. Barrier layer 10 is a non-magnetic insulating material,preferably made of aluminum-oxide, which is generally less than 10Angstroms (Å) in thickness.

As indicated in FIG. 4, a trackwidth W_(T) of the magnetic head isdefined by the dimension of emitter region 5, base region 15, andcollector region 20 along the y-axis, while a stripe height H_(S) of themagnetic head is defined by the dimension of emitter region 5 along thex-axis. A sensing plane 1020 of TTM 400 is defined along sides of baseregion 15, collector region 20, and emitter region 5. This sensing plane1020 is at an air bearing surface (ABS) when TTM 400 is embodied in amagnetic head. A non-magnetic insulator layer 1012 is offset behindsensing plane 1020 and adjacent collector region 20 and base region 15.Insulator layer 1012 may be, for example, an oxide materials such asalumina. An emitter lead 35, which may be embodied as a ferromagnetic(FM) shield for TTM 400, is positioned in contact with emitter region 5at sensing plane 1020. Emitter lead 35 serves as the electricalconnection for emitter region 5 to an external lead (not visible in FIG.4). A base lead 36 is positioned in contact with base region 15 behindsensing plane 1020. Base lead 36 and a collector lead (not visible inFIG. 4) are preferably not formed along sensing plane 1020. Note thatadditional or alternative leads may be formed in the TTM, which has atleast three leads.

The TTM allows hot electrons emitted from emitter region 5 to travelthrough to base region 15 to reach collector region 20, which collectsthe magnetocurrent (i.e. collects the electrons). In operation, thedevice acts as a hot spin electron filter whereby barrier region 10between emitter region 5 and base region 15 operates to selectivelyallow the hot electrons to pass on through to base region 15 and then onthrough collector region 20. When TTM 400 is not functioning, the deviceis in a known quiescent state. In this case, the magnetization of thefree layer which comprises all or part of base region 15 is parallel tothe ABS plane. The direction of this magnetization depends on thedirection of the magnetic field produced by a pinned layer (not visible)formed adjacent the free layer. The scattering of electrons within thefree layer is dependent upon the orientation of the magnetization withinthe free layer. For example, if the magnetization is pointing in theparallel direction relative to the pinned layer (i.e. parallel to theABS plane), then the electrons are not scattered as much as compared tothe case where the free layer is antiparallel relative to the pinnedlayer. The performance of the device may be different depending upon therelative configuration of emitter region 5, the free layer, and the hardbias layer.

Since it is advantageous to form a very thin base region 15 (e.g.between about 20-200 Å) for increased areal recording densities, baseregion 15 will have a relatively large electrical resistance if nothingis done to reduce it. With the trackwidth (TW) of the magnetic headbeing defined at between about 10 and 100 nanometers (nm) (e.g.approximately 50 nm), the electrical resistance of base region 15 may bemuch greater than 100Ω. Thus, as the sense current passes through baseregion 15 from emitter lead 35 to base lead 36, base region 15 may bevulnerable to damage or failure (e.g. it could “blow” like a fuse). Arelatively large resistance of base region 15 also raises the noisefloor for the TTM 400 such that a much larger input signal for TTM 400would be required for suitable operation.

Accordingly, a metal layer 1050 is formed in TTM 400 so as to be offsetfrom sensing plane 1020 and in-plane and in contact with magneticmaterials of base region 15. In FIG. 4, metal layer 1050 is formed incontact with insulator layer 1012 but not in contact with base lead 36.This metal layer 1050 is thicker than any other metal film which may beformed within base region 15 itself; metal layer 1050 is preferablyformed to a thickness of between 50-500% (at least 50%) of the totalthickness of base region 15. For example, metal layer 1050 may be formedto a thickness of between about 100-1000 Å. Note that metal layer 1050stops where insulator layer 1012 ends; it does not extend over collectorregion 20. If a metal were formed over a collector via 22 wherecollector region 20 meets base region 15, it would cause a short betweenthe two leads. As an alternative to or in combination with metal layer1050, TTM 400 of FIG. 4 also shows that a metal layer 1050 may be formedadjacent and between (in contact with) insulator layer 1012 and baselead 36. In addition, an alternative TTM 500 of FIG. 5 shows that metallayer 1050 may be alternatively formed along a top surface of baseregion 15 and in contact with base lead, not formed in contact withinsulator layer 1012, and otherwise being the same as that shown anddescribed in relation to FIG. 4.

Such metal layers of FIGS. 4 and 5 reduce the electrical resistance ofbase region 15, which is advantageous as it serves to reduce signalnoise in TTM 400 by lowering the noise floor. Preferably, metal layer1050 has an electrical resistivity of less than 10 μΩ-centimeter (cm).For example, metal layer 1050 may be made of copper (Cu), gold (Au),ruthenium (Ru), alloys and/or combinations thereof. Copper has anapproximate electrical resistivity of 2 μΩ-cm, gold has an approximateelectrical resistivity of 5 μΩ-cm, and ruthenium has an approximateelectrical resistivity of 7 μΩ-cm. In comparison, base region 15 alonewith magnetic materials (e.g. ferromagnetic (FM) materials such asnickel-iron (NiFe) and cobalt-iron (CoFe) may have an electricalresistivity of between about 18-40 μΩ-cm. On the other hand, theelectrical resistivity of combined materials for base region 15 andmetal layer 1050 may be between about 2-18 μΩ-cm. As a result, thecombined layer may have a combined electrical resistance of betweenabout 5-100 Ω.

As an alternative to or in combination with the metal layers of FIG. 4or 5, a TTM 600 of FIG. 6 shows that a metal layer 1054 may be formed inplane and in contact with magnetic materials of emitter region 5. ThisTTM 600 of FIG. 6 has a different construction than that shown anddescribed in relation to FIGS. 4 and 5. Comparing the embodiment of FIG.6 with that of FIG. 4, emitter region 5 extends much further behindsensing plane 1020. Emitter lead 35 of FIG. 6 is located where theprevious base lead in FIG. 4 was formed and base lead 36 of FIG. 6 islocated where the previous metal layer in FIG. 4 was formed. Again, thismetal layer 1054 is formed in plane and in contact with magneticmaterials of emitter region 5. Metal layer 1054 is also formed incontact with emitter lead 35. This metal layer 1054 is offset fromsensing plane 1020 and does not make contact with collector region 20.Otherwise metal layer 1054 of FIG. 6 may be the same or similar to thatdescribed in relation to FIG. 4, where it reduces the electricalresistance of emitter region 5 with the same or similar results.

FIG. 7A is a sensing plane (or ABS) view of one embodiment of a threeterminal magnetic sensor (TTM) 700 a of the present application. TTM 700a of FIG. 7A has the general structure and functionality as describedabove in relation to the drawings, with or without having the metallayer for reduced lead resistance. As shown in FIG. 7A, TTM 700 a has anemitter region 702, a base region 704, and a collector region 706. Afirst barrier layer 708 is located between emitter region 702 and baseregion 704, and a second barrier layer 726 is located between collectorregion 706 and base region 704. First barrier layer 708 may be aSchottky barrier (electrically conductive material) or a tunnel barrier(insulator material). Similarly, second barrier layer 726 may be aSchottky barrier (electrically conductive material) or a tunnel barrier(insulator material). Emitter region 702 has one or more emitter layers728 which may be or include a silicon layer or a ferromagnetic (FM)layer such as nickel-iron. Collector region 706 has one or morecollector layers 730 which may be or include a silicon layer or an FMlayer such as nickel-iron.

In this embodiment, base region 704 includes a free layer structure 714,a pinned layer structure 712, an antiferromagnetic (AFM) pinning layer718, a first non-magnetic spacer layer 720, an in-stack longitudinalbiasing layer (LBL) structure 716, and a second non-magnetic spacerlayer 726. Pinned layer structure 712 is adjacent first non-magneticspacer layer 720, which is in turn adjacent free layer structure 714. AnFM pinned layer of pinned layer structure 712 is magnetically pinned byexchange-coupling with AFM pinning layer 718. AFM pinning layer 718 islocated between and adjacent pinned layer structure 712 and firstbarrier layer 708. The pinning field generated by AFM pinning layer 718should be greater than demagnetizing fields to ensure that themagnetization direction of the FM pinned layer remains fixed duringapplication of external fields (e.g. fields from bits recorded on thedisk). The magnetization of free layer structure 714 is not fixed and isfree to rotate in response to the field from the information recorded onthe magnetic medium (i.e. the signal field).

Pinned layer structure 712 may be a single FM layer or, alternatively, amulti-layer structure. In particular, pinned layer structure 712 may bean antiparallel (AP) pinned layer structure as shown in FIG. 11. In FIG.11, an AP pinned layer structure 1100 includes a first AP pinned layer1102, a second AP pinned layer 1104, and an AP coupling layer 1106formed between first and second AP pinned layers 1102 and 1104. First APpinned layer 1102, for example, may be the layer that isexchange-coupled to and pinned by the AFM pinning layer 718. By strongantiparallel coupling between the first and second AP pinned layers 1102and 1104, the magnetic moment of second AP pinned layer 1104 is madeantiparallel to the magnetic moment of first AP pinned layer 1102.

In-stack LBL structure 716 is located adjacent and between free layerstructure 714 and second barrier layer 726. Being formed “in-stack” withthe sensor layers, LBL structure 716 is formed within the central regionof the sensor but not within side regions thereof. LBL structure 716includes a pinned layer structure 722, an AFM pinning layer 724, and anon-magnetic spacer layer 726. AFM pinning layer 724 of LBL structure716 is located between and adjacent pinned layer structure 722 andsecond barrier layer 710. FM pinned layer 712 is magnetically pinned byexchange-coupling with an AFM pinning layer 718. In particular, AFMpinning layer 724 pins a magnetic moment of pinned layer structure 722parallel to the ABS and parallel to the planes of the sensor layers asindicated. Spacer layer 726 causes pinned layer structure 722 and freelayer structure 714 to be physically separated but in close proximity toeach other. Because of pinned layer structure 722, the magnetic momentof free layer structure 714 is magnetically stabilized parallel to theABS and parallel to the major planes of the sensor as indicated by thedashed arrows. This biasing is uniform from the sides of free layerstructure 714 so that the biasing does not cause a limitation on narrowtrack width sensors. Pinned layer structure 722 may be a single FM layeror alternatively a multi-layer structure, and may include an AP pinnedstructure as previously shown and described in relation to FIG. 11.Spacer layer 726 may be chosen to provide either weakly ferromagneticcoupling or AP-coupling between pinned layer structure 722 and freelayer structure 714.

Note that AFM pinning layer 724 of LBL structure 716 should preferablymagnetically pin at a different temperature than AFM pinning layer 718.The reason is so that, during TTM fabrication, the pinning achieved forAFM pinning layer 724 will not be adversely affected by the subsequentpinning process utilized for AFM pinning layer 718. As is known, thepinning of AFM pinning layers is typically achieved by heating the AFMmaterials to a predetermined temperature and applying a magnetic fieldat the same time. Preferably, to obtain the difference in pinningtemperatures, AFM pinning layer 724 is made of a different material thanthat of AFM pinning layer 718. For example, AFM pinning layer 718 may bemade of platinum-manganese (PtMn) and AFM pinning layer 724 may be madeof iridium-manganese (IrMn). A similar result may be achieved byutilizing the same materials for AFM pinning layers 718 and 724 withdifferent thicknesses. More generally, the choice of any AFM materialand its thickness may vary. The AFM layers may be the same material oralternatively have the same thickness. Preferably, the AFM layers aremade of different materials and have different thicknesses.

Exemplary thicknesses and materials of TTM 700 a are indicated in FIG.7A. In-stack longitudinal bias layer structure 716 has AFM pinning layer724 made of platinum-manganese (PtMn) with a thickness of about 150Angstroms, pinned layer 724 made of cobalt-iron (CoFe) with a thicknessof about 20 Angstroms, and spacer layer 726 made of tantalum (Ta) with athickness of about 20 Angstroms. AFM pinning layer 718 is made ofiridium-manganese (IrMn) with a thickness of about 80 Angstroms, pinnedlayer 712 made of cobalt-iron (CoFe) with a thickness of about 20Angstroms, and spacer layer 720 made of copper (Cu) with a thickness ofabout 20 Angstroms. Free layer structure 714 is made of nickel-iron(NiFe) with a thickness of about 40 Angstroms.

Preferably, there is a predetermined relationship established betweenthe magnetic thickness of the pinned layer structure 722 of LBLstructure 716 and the magnetic thickness of free layer structure 714.Preferably, the magnetic thickness of pinned layer structure 722 is madeto be substantially the same as the magnetic thickness of free layerstructure 714. However, the magnetic thickness of the pin layer may bebetween 50-500% of the thickness of the free layer.

One variation of the TTM 700 a of FIG. 7A is a TTM 700 b shown in FIG.7B. TTM 700 b of FIG. 7B is the same as TTM 700 a of FIG. 7A except thatthe layers in base region 704 are inverted as shown. Another variationof the TTM 700 a of FIG. 7A is a TTM 700 c shown in FIG. 7C. TTM 700 cof FIG. 7C is the same as TTM 700 a of FIG. 7A except that base region704 c includes a self-pinned layer structure 712 c as the pinned layerstructure. For TTM 700 c, the AFM pinning layer 718 of the TTM 700 a ofFIG. 7A is not needed for pinning purposes. A sensor of the self-pinnedtype relies on magnetostriction of the self-pinned structure and the ABSstress for a self-pinning effect. The AFM pinning layer, which istypically as thick as 150 Angstroms, is no longer necessary for pinningpurposes so that a thinner sensor can be made. TTM 700 d of FIG. 7D isanother structural variation where LBL structure 716 d also has aself-pinned layer structure 722 d. Note that the self-pinned layerstructure 722 d of FIG. 7D may include one or multiple layers ofmaterials. In this variation, structure 712 c may or may not beself-pinned.

FIG. 8A is a sensing plane (or ABS) view of another embodiment of a TTM800 a of the present application. TTM 800 a of FIG. 8A has the generalstructure and functionality of the TTM shown and described above inrelation to the drawings, with or without having the metal layer forreduced lead resistance. As shown in FIG. 8A, TTM 800 a has an emitterregion 802, a base region 804, and a collector region 806. A firstbarrier layer 808 is located between emitter region 802 and base region804, and a second barrier layer 826 is located between collector region806 and base region 804. First barrier layer 808 may be a Schottkybarrier (electrically conductive material) or a tunnel barrier(insulator material). Similarly, second barrier layer 826 may be aSchottky barrier (electrically conductive material) or a tunnel barrier(insulator material). Emitter region 802 has one or more emitter layers828 which may be or include a silicon layer or an FM layer such asnickel-iron.

In this embodiment, base region 804 includes a free layer structure 814,a pinned layer structure 812, an AFM pinning layer 818, and anon-magnetic spacer layer 820. Pinned layer structure 812 is adjacentfirst non-magnetic spacer layer 820, which is in turn adjacent freelayer structure 814. An FM pinned layer of pinned layer structure 812 ismagnetically pinned by exchange-coupling with AFM pinning layer 818. AFMpinning layer 818 is located between and adjacent pinned layer structure812 and first barrier layer 808. The pinning field generated by AFMpinning layer 818 should be greater than demagnetizing fields to ensurethat the magnetization direction of the FM pinned layer remains fixedduring application of external fields (e.g. fields from bits recorded onthe disk). The magnetization of free layer structure 814 is not fixedand is free to rotate in response to the field from the informationrecorded on the magnetic medium (i.e. the signal field). Pinned layerstructure 812 may be a single FM layer or, alternatively, a multi-layerstructure. In particular, pinned layer structure 812 may be an AP pinnedlayer structure as shown and described earlier in relation to FIG. 11.

Collector region 806 has an in-stack LBL structure 816. Collector region806 may also have one or more other collector layers 830 which may be orinclude a silicon layer or an FM layer such as nickel-iron. Being formed“in-stack” with the sensor layers, LBL structure 816 of collector region806 is formed within the central region of the sensor but not withinside regions thereof. LBL structure 816 includes a pinned layerstructure 828 and an AFM pinning layer 824. Second barrier layer 826 isformed between LBL structure 816 and free layer structure 814, causingpinned layer structure 822 and free layer structure 814 to be physicallyseparated but in close proximity to each other. As apparent, secondbarrier layer 826 simultaneously serves as a spacer layer for LBLstructure 816; no separate spacer layer is needed. Note that since baseregion 806 does not contain LBL structure 816, base region 806 has asmaller thickness for an improved signal in the TTM 800.

Pinned layer structure 822 of LBL structure 816 is magnetically pinnedby exchange-coupling with AFM pinning layer 824. In particular, AFMpinning layer 824 pins a magnetic moment of pinned layer structure 822parallel to the ABS and parallel to the planes of the sensor layers asindicated. Because of pinned layer structure 822, the magnetic moment offree layer structure 814 is magnetically stabilized parallel to the ABSand parallel to the major planes of the sensor as indicated by thedashed arrows. This biasing is uniform from the sides of free layerstructure 814 so that the biasing does not cause a limitation on narrowtrack width sensors. Pinned layer structure 822 may be a single FM layeror alternatively a multi-layer structure, and may include an AP pinnedstructure as previously shown and described in relation to FIG. 11.

Note that AFM pinning layer 824 of LBL structure 816 should preferablymagnetically pin at a different temperature than AFM pinning layer 818.The reason is so that, during TTM fabrication, the pinning achieved forAFM pinning layer 824 will not be adversely affected by the subsequentpinning process utilized for AFM pinning layer 818. As is known, thepinning of AFM pinning layers is typically achieved by heating the AFMmaterials to a predetermined temperature and applying a magnetic fieldat the same time. Preferably, to obtain the difference in pinningtemperatures, AFM pinning layer 824 is made of a different material thanthat of AFM pinning layer 818. For example, AFM pinning layer 818 may bemade of platinum-manganese (PtMn) and AFM pinning layer 824 may be madeof iridium-manganese (IrMn). A similar result may be achieved byutilizing the same materials for AFM pinning layers 818 and 824 withdifferent thicknesses. More generally, the choice of any AFM materialand its thickness may vary. The AFM layers may be the same material oralternatively have the same thickness. Preferably, the AFM layers aremade of different materials and have different thicknesses.

Exemplary thicknesses and materials of TTM 800 a are indicated in FIG.8A. In-stack longitudinal bias layer structure 816 has AFM pinning layer824 made of platinum-manganese (PtMn) with a thickness of about 180Angstroms and pinned layer 822 made of cobalt-iron (CoFe) with athickness of about 20 Angstroms. AFM pinning layer 818 is made ofiridium-manganese (IrMn) with a thickness of about 80 Angstroms, pinnedlayer 812 made of cobalt-iron (CoFe) with a thickness of about 20Angstroms, and spacer layer 820 made of copper (Cu) with a thickness ofabout 20 Angstroms. Free layer structure 814 is made of nickel-iron(NiFe) with a thickness of about 40 Angstroms.

Preferably, there is a predetermined relationship established betweenthe magnetic thickness of the pinned layer structure 822 of LBLstructure 816 and the magnetic thickness of free layer structure 814. Inparticular, the magnetic thickness of pinned layer structure 822 is madeto be substantially the same as the magnetic thickness of free layerstructure 814. However, the magnetic thickness of the pinned layer maybe between 50-500% of the thickness of the free layer.

One variation of the TTM 800 a of FIG. 8A is a TTM 800 b shown in FIG.8B. TTM 800 b of FIG. 8B is the same as TTM 800 a of FIG. 8A except thatthe layers are inverted as shown, such that an emitter region 802 bincludes in-stack LBL structure 816 and base region 804 b includes freelayer structure 814 and pinned layer structure 812. Another variation ofthe TTM 800 a of FIG. 8A is a TTM 800 c shown in FIG. 8C. TTM 800 c ofFIG. 8C is the same as TTM 800 a of FIG. 8A except that a base region804 c includes a self-pinned layer structure 812 c as the pinned layerstructure. For TIM 800 c, the AFM pinning layer 818 of the TIM 800 a ofFIG. 8A is not needed for pinning purposes. A sensor of the self-pinnedtype relies on magnetostriction of the self-pinned structure and the ABSstress for a self-pinning effect. The AFM pinning layer, which istypically as thick as 150 Angstroms, is no longer necessary for pinningpurposes so that a thinner sensor can be made. TTM 800 d of FIG. 8D isanother structural variation where LBL structure 816 d also has aself-pinned layer structure 822 d. Note that the self-pinned layerstructure 822 d of FIG. 8D may include one or multiple layers ofmaterials. In this variation, structure 812 c may or may not beself-pinned.

FIG. 9A is a sensing plane (or ABS) view of yet another embodiment of aTTM 900 a of the present application. TTM 900 a of FIG. 9A has thegeneral structure and functionality of the TTM shown and described abovein relation to the drawings, with or without having the metal layer forreduced lead resistance. As shown in FIG. 9A, TTM 900 a has an emitterregion 902, a base region 904, and a collector region 906. A firstbarrier layer 920 is located between emitter region 902 and base region904, and a second barrier layer 926 is located between collector region906 and base region 904. First barrier layer 920 may be a Schottkybarrier (electrically conductive material) or a tunnel barrier(insulator material). Similarly, second barrier layer 926 may be aSchottky barrier (electrically conductive material) or a tunnel barrier(insulator material).

In this embodiment, base region 904 consists of a free layer structure914. Since free layer structure 914 is the only structure providedwithin base region 904, the base region has a relatively small thicknessfor an improved signal in the TTM 900. Emitter region 902 has a pinnedlayer structure 912 and an AFM pinning layer 918. Emitter region 902 mayalso have one or more other emitter layers 928 which may be or include asilicon layer or an FM layer such as nickel-iron. Pinned layer structure912 is adjacent first barrier layer 920, which is in turn adjacent freelayer structure 914. As apparent, first barrier layer 920 simultaneouslyserves as a spacer layer between pinned layer structure 912 and freelayer structure 914.

An FM pinned layer of pinned layer structure 912 is magnetically pinnedby exchange-coupling with AFM pinning layer 918, which is formedadjacent pinned layer structure 912. The pinning field generated by AFMpinning layer 918 should be greater than demagnetizing fields to ensurethat the magnetization direction of the FM pinned layer remains fixedduring application of external fields (e.g. fields from bits recorded onthe disk). The magnetization of free layer structure 914 is not fixedand is free to rotate in response to the field from the informationrecorded on the magnetic medium (i.e. the signal field). Pinned layerstructure 912 may be a single FM layer or, alternatively, a multi-layerstructure. In particular, pinned layer structure 912 may be an AP pinnedlayer structure as shown and described earlier in relation to FIG. 11.

Collector region 906 has an in-stack LBL structure 916. Collector region906 may also have one or more other collector layers 930 which may be orinclude a silicon layer or an FM layer such as nickel-iron. Being formed“in-stack” with the sensor layers, LBL structure 916 of collector region906 is formed within the central region of the sensor but not withinside regions thereof. LBL structure 916 includes a pinned layerstructure 922 and an AFM pinning layer 924. Second barrier layer 926 isformed between LBL structure 916 and free layer structure 914, causingpinned layer structure 922 and free layer structure 914 to be physicallyseparated but in close proximity to each other. As apparent, secondbarrier layer 926 simultaneously serves as a spacer layer for LBLstructure 916; no separate spacer layer is needed to provide suchseparation.

Pinned layer structure 922 is magnetically pinned by exchange-couplingwith AFM pinning layer 924. In particular, AFM pinning layer 924 pins amagnetic moment of pinned layer structure 922 parallel to the ABS andparallel to the planes of the sensor layers as indicated. Because ofpinned layer structure 922 the magnetic moment of free layer structure914 is magnetically stabilized parallel to the ABS and parallel to themajor planes of the sensor as indicated by the dashed arrows. Thisbiasing is uniform from the sides of free layer structure 914 so thatthe biasing does not cause a limitation on narrow track width sensors.Pinned layer structure 922 may be a single FM layer or alternatively amulti-layer structure, and may include an AP pinned structure aspreviously shown and described in relation to FIG. 11.

Note that AFM pinning layer 924 of LBL structure 916 should preferablymagnetically pin at a different temperature than AFM pinning layer 918.The reason is so that, during TTM fabrication, the pinning achieved forAFM pinning layer 924 will not be adversely affected by the subsequentpinning process utilized for AFM pinning layer 918. As is known, thepinning of AFM pinning layers is typically achieved by heating the AFMmaterials to a predetermined temperature and applying a magnetic fieldat the same time. Preferably, to obtain the difference in pinningtemperatures, AFM pinning layer 924 is made of a different material thanthat of AFM pinning layer 918. For example, AFM pinning layer 918 may bemade of platinum-manganese (PtMn) and AFM pinning layer 924 may be madeof iridium-manganese (IrMn). A similar result may be achieved byutilizing the same materials for AFM pinning layers 918 and 924 withdifferent thicknesses. More generally, the choice of any AFM materialand its thickness may vary. The AFM layers may be the same material oralternatively have the same thickness. Preferably, the AFM layers aremade of different materials and have different thicknesses.

Exemplary thicknesses and materials of TTM 900 a are indicated in FIG.9A. In-stack longitudinal bias layer structure 916 has AFM pinning layer924 made of platinum-manganese (PtMn) with a thickness of about 150Angstroms and pinned layer 922 made of cobalt-iron (CoFe) with athickness of about 20 Angstroms. AFM pinning layer 918 is made ofiridium-manganese (IrMn) with a thickness of about 80 Angstroms andpinned layer 912 made of cobalt-iron (CoFe) with a thickness of about 40Angstroms. Free layer structure 914 is made of nickel-iron (NiFe) with athickness of about 40 Angstroms.

Preferably, there is a predetermined relationship established betweenthe magnetic thickness of the pinned layer structure 922 of LBLstructure 916 and the magnetic thickness of free layer structure 914. Inparticular, the magnetic thickness of pinned layer structure 922 is madeto be substantially the same as the magnetic thickness of free layerstructure 914. However, the magnetic thickness of the pinned layer maybe between 50-500% of the thickness of the free layer.

One variation of the TTM 900 a of FIG. 9A is a TTM 900 b shown in FIG.9B. TTM 900 b of FIG. 9B is the same as TTM 900 a of FIG. 9A except thatthe layers are inverted as shown, such that an emitter region 902 bincludes in-stack LBL structure 916 and collector region 906 b includespinned layer structure 918. Another variation of the TTM 900 a of FIG.9A is a TTM 900 c shown in FIG. 9C. TTM 900 c of FIG. 9C is the same asTTM 900 a of FIG. 9A except that emitter region 902 c includes aself-pinned layer structure 912 c as the pinned layer structure. For TTM900 c, the AFM pinning layer 918 of the TTM 900 a of FIG. 9A is notneeded for pinning purposes. A sensor of the self-pinned type relies onmagnetostriction of the self-pinned structure and the ABS stress for aself-pinning effect. The AFM pinning layer, which is typically as thickas 150 Angstroms, is no longer necessary for pinning purposes so that athinner sensor can be made. TTM 900 d of FIG. 9D is another structuralvariation where LBL structure 916 d also has a self-pinned layerstructure 922 d. Note that the self-pinned layer structure 922 d of FIG.9D may include one or multiple layers of materials. In this variation,structure 912 c may or may not be self-pinned.

FIG. 10 is a sensing plane (or ABS) view of yet another embodiment of aTTM 1000 of the present application. TTM 1000 of FIG. 10 has the generalstructure and functionality of the TTM shown and described abovegenerally in relation to the drawings, with or without having the metallayer for reduced lead resistance. Specifically, TTM 1000 is a specificembodiment of that shown and described in relation to FIG. 9A and is ofthe double tunnel junction type. As shown in FIG. 10, TTM 1000 has anemitter region 1002, a base region 1004, and a collector region 1006. Afirst insulative tunnel barrier layer 1008 is located between emitterregion 1002 and base region 1004, and a second insulative tunnel barrierlayer 1026 is located between collector region 1006 and base region1004. Since TTM 1000 is of the double tunnel junction type, first andbarrier layers 1008 and 1026 are insulative tunnel barriers made of asuitable electrically insulative material (e.g. Al₂O₃ or alumina).

In this embodiment, base region 1004 consists of a free layer structure1014. Since free layer structure 1014 is the only structure providedwithin base region 1004, the base region has a relatively smallthickness for an improved signal in the TTM 1000. Emitter region 1002has a pinned layer structure 1012 and an AFM pinning layer 1018. Emitterregion 1002 may also have one or more other emitter layers 1028 whichmay be or include a silicon layer or an FM layer such as nickel-iron.Pinned layer structure 1012 is adjacent first insulative tunnel barrierlayer 1008, which is in turn adjacent free layer structure 1014. Asapparent, first insulative tunnel barrier layer 1008 simultaneouslyserves as a spacer layer between pinned layer structure 1012 and freelayer structure 1014.

An FM pinned layer of pinned layer structure 1012 is magnetically pinnedby exchange-coupling with AFM pinning layer 1018, which is formedadjacent pinned layer structure 1012. The pinning field generated by AFMpinning layer 1018 should be greater than demagnetizing fields to ensurethat the magnetization direction of the FM pinned layer remains fixedduring application of external fields (e.g. fields from bits recorded onthe disk). The magnetization of free layer structure 1014 is not fixedand is free to rotate in response to the field from the informationrecorded on the magnetic medium (i.e. the signal field). Pinned layerstructure 1012 may be a single FM layer or, alternatively, a multi-layerstructure. In particular, pinned layer structure 1012 may be an APpinned layer structure as shown and described earlier in relation toFIG. 11. The FM pinned layer of pinned layer structure 1012 mayalternatively be “self-pinned” where AFM pinning layer 1018 is notneeded for pinning purposes, as described earlier above.

Collector region 1006 has an in-stack LBL structure 1016. Collectorregion 1006 may also have one or more other collector layers 1030 whichmay be or include a silicon layer or an FM layer such as nickel-iron.Being formed “in-stack” with the sensor layers, LBL structure 1016 ofcollector region 1006 is formed within the central region of the sensorbut not within side regions thereof. LBL structure 1016 includes apinned layer structure 1022 and an AFM pinning layer 1024. Secondinsulative tunnel barrier layer 1026 is formed between LBL structure1016 and free layer structure 1014, causing pinned layer structure 1022and free layer structure 1014 to be physically separated but in closeproximity to each other. As apparent, second insulative tunnel barrierlayer 1026 simultaneously serves as a spacer layer for LBL structure1016; no separate spacer layer is needed to provide such separation.

Pinned layer structure 1022 is magnetically pinned by exchange-couplingwith AFM pinning layer 1024. In particular, AFM pinning layer 1024 pinsa magnetic moment of pinned layer structure 1022 parallel to the ABS andparallel to the planes of the sensor layers as indicated. Because ofpinned layer structure 1022, the magnetic moment of free layer structure1014 is magnetically stabilized parallel to the ABS and parallel to themajor planes of the sensor as indicated by the dashed arrows. Thisbiasing is uniform from the sides of free layer structure 1014 so thatthe biasing does not cause a limitation on narrow track width sensors.Pinned layer structure 1022 may be a single FM layer or alternatively amulti-layer structure, and may include an AP pinned structure aspreviously shown and described in relation to FIG. 11.

Note that AFM pinning layer 1024 of LBL structure 1016 should preferablymagnetically pin at a different temperature than AFM pinning layer 1018.The reason is so that, during TTM fabrication, the pinning achieved forAFM pinning layer 1024 will not be adversely affected by the subsequentpinning process utilized for AFM pinning layer 1018. As is known, thepinning of AFM pinning layers is typically achieved by heating the AFMmaterials to a predetermined temperature and applying a magnetic fieldat the same time. Preferably, to obtain the difference in pinningtemperatures, AFM pinning layer 1024 is made of a different materialthan that of AFM pinning layer 1018. For example, AFM pinning layer 1018may be made of platinum-manganese (PtMn) and AFM pinning layer 1024 maybe made of iridium-manganese (IrMn). A similar result may be achieved byutilizing the same materials for AFM pinning layers 1018 and 1024 withdifferent thicknesses. More generally, the choice of any AFM materialand its thickness may vary. The AFM layers may be the same material oralternatively have the same thickness. Preferably, the AFM layers aremade of different materials and have different thicknesses.

Exemplary thicknesses and materials of TTM 1000 are indicated in FIG.10. In-stack longitudinal bias layer structure 1016 has AFM pinninglayer 1024 made of platinum-manganese (PtMn) with a thickness of about150 Angstroms and pinned layer 1022 made of cobalt-iron (CoFe) with athickness of about 20 Angstroms. AFM pinning layer 1018 is made ofiridium-manganese (IrMn) with a thickness of about 80 Angstroms andpinned layer 1012 made of cobalt-iron (CoFe) with a thickness of about40 Angstroms. Free layer structure 1014 is made of nickel-iron (NiFe)with a thickness of about 40 Angstroms.

A TTM of the present application may be fabricated using conventionallithographic techniques, as now described. In the following description,a TTM of the type shown and described in relation to FIG. 4 and FIG. 7Ais specifically made; these techniques are easily applied for thefabrication of all TTM types. Referring to FIG. 12A, collector region 20is shown with an insulating oxide layer 1010/1012 deposited thereon. Aresist pattern 43 is then used to remove a middle portion of theinsulating layer 1010/1012 which creates, as shown in FIG. 12B, a via 44down to the semiconductor substrate 20 as well as insulating layers 1010and 1012. The removal of the insulating layer materials may be performedusing conventional etching techniques. Optionally, a metal layer 1050 isthen formed over at least a portion of insulating layer 1012. Metallayer 1050 may be formed using sputter-deposition or electroplatingsteps, as well as lithography steps with a patterned resist and etching.An air bearing surface (ABS) 11 of the sensor structure is representedby a dotted line in FIGS. 13A and 13B as well as in the subsequentdrawings.

In FIG. 14A, a sensor stack 18 is formed over insulating layers 1010 and1012, into via 44, and over metal layer 1050. Sensor stack 18 includesbase region 15 and emitter region 5, with the barrier regions (e.g.barrier region 10) deposited in the stack where appropriate. Behind thesensing plane, base region 15 is formed over and in contact with metallayer 1050. The top-down view of FIG. 14B illustrates the upper cap ofsensor stack 18, which is top the surface of emitter region 5. Next, asdepicted in FIGS. 15A and 15B, another resist 46 is used to patternsensor stack 18, where portions of emitter region 5 are removed usingknown techniques such as ion milling or reactive ion etching (RIE). Thisexposes base layer 15 along the sides and defines the stripe heightH_(S) of the device. As shown in FIGS. 16A and 16B, an insulator 25(such as alumina) is then filled in the areas over exposed base layer15.

In the next stage of processing, as illustrated in FIGS. 17A and 17B, apatterned resist 47 is used to pattern the structure along a trackwidth(TW) axis 1600 with an etch. Patterned resist 47 is best viewed in thetop-down view of FIG. 12B where the exposed portions of insulator 25 andemitter 5 are shown. Once the exposed material is removed, an insulatinglayer 29 is deposited as depicted in the ABS view of FIG. 18A and a topplan view of FIG. 18B. In the ABS view of FIG. 19A and in FIG. 19B,portions of insulator layer 29 are removed along with portions of refillalumina 25 and base region 15, such that only emitter region 5 and aremaining portion of base region 15 are located between insulator layer29. Another resist 48 is then used to pattern the device and anotherinsulator 38 fills the exposed portions. FIGS. 20A and 20B illustratethe device where yet another resist 49 used to pattern (etch) a via 56to base region 15 and a via (not visible) to collector region 20. Thisstep may etch through metal layer 1050 as shown or, alternatively,refrain from etching through metal layer 1050. After the patterning iscompleted, the transistor device is plated with emitter lead 35 and baselead 36 as shown in FIGS. 21A and 21B, wherein these leads 35, 36 arepreferably made of nickel-iron (NiFe). Other leads, such as thecollector lead (not shown) can also be included in this lead-platingstep.

Final Comments. As described herein, a three terminal magnetic sensor(TTM) of the present application which is suitable for use in a magnetichead has a base region, a collector region, and an emitter region. Afirst barrier layer separates the emitter region from the base region,and a second barrier layer separates the collector region from the baseregion. A sensing plane is defined along sides of the base region, thecollector region, and the emitter region. The base region consists of afree layer structure so as to have a relatively small thickness. Apinned layer structure is made part of the emitter region. An in-stacklongitudinal biasing layer (LBL) structure which magnetically biases thefree layer structure is made part of the collector region. In onevariation, the emitter region has the in-stack LBL structure and thecollector region has the pinned layer structure. The TTM may comprise aspin valve transistor (SVT), a magnetic tunnel transistor (MTT), or adouble junction structure.

A disk drive of the present application includes a slider, a magnetichead carried on the slider, a write head portion of the magnetic head,and a read head portion of the magnetic head which includes a threeterminal magnetic sensor (TTM). The TTM has a base region, a collectorregion, and an emitter region. A first barrier layer separates theemitter region from the base region, and a second barrier layerseparates the collector region from the base region. An air bearingsurface (ABS) plane is defined along sides of the base region, thecollector region, and the emitter region. The base region consists of afree layer structure so as to have a relatively small thickness. Apinned layer structure is made part of the emitter region. An in-stacklongitudinal biasing layer (LBL) structure which magnetically biases thefree layer structure is made part of the collector region. The TTM maycomprise a spin valve transistor (SVT), a magnetic tunnel transistor(MTT), or a double junction structure.

It is to be understood that the above is merely a description ofpreferred embodiments of the invention and that various changes,alterations, and variations may be made without departing from the truespirit and scope of the invention as set for in the appended claims. Forexample, although the TTM is described as a three-leaded device, it mayactually have three or more leads. Few if any of the terms or phrases inthe specification and claims have been given any special particularmeaning different from the plain language meaning to those ordinarilyskilled in the art, and therefore the specification is not to be used todefine terms in an unduly narrow sense.

1. A three terminal magnetic sensor (TTM), comprising: a sensor stackstructure comprising a base region, a collector region, and an emitterregion; a first barrier layer located between the emitter region and thebase region; a second barrier layer located between the collector regionand the base region; a plurality of terminals of the TTM comprising abase lead coupled to the base region, a collector lead coupled to thecollector region, and an emitter lead coupled to the emitter region; thecollector region comprising a layer of semiconductor material; the baseregion being made of ferromagnetic materials and comprising a free layerstructure; one of the emitter region and the collector region comprisinga pinned layer structure; the other one of the emitter region and thecollector region comprising an in-stack longitudinal biasing layerstructure; the in-stack longitudinal biasing layer structure comprisinga first ferromagnetic (FM) pinned layer and a first antiferromagnetic(AFM) pinning layer which magnetically pins the first FM pinned layer;the in-stack longitudinal biasing layer structure being formed in stackwith the sensor stack structure and having a magnetic moment that isparallel to a sensing plane of the TTM for longitudinally biasing thefree layer structure; the pinned layer structure including a second FMpinned layer and a second AFM pinning layer which magnetically pins thesecond FM pinned layer; an insulator layer which is offset from thesensing plane and in between the base region and the collector region;and a layer of metal which is offset from the sensing plane and incontact with the ferromagnetic materials of the base region, the layerof metal having an electrical resistivity of less than 10 uΩ-centimetersso that a combined electrical resistivity of the base region is betweenabout 2-18 uΩ-centimeters.
 2. The TTM of claim 1, wherein one of thebarrier layers serves as a non-magnetic spacer layer between the freelayer structure and the in-stack longitudinal biasing layer structure.3. The TTM of claim 1, wherein one of the barrier layers serves as anon-magnetic spacer layer between the free layer structure and thepinned layer structure.
 4. The TTM of claim 1, further comprising: thefirst AFM pinning layer being formed of a first material; and the secondAFM pinning layer being formed of a second material that is not presentin the first AFM pinning layer, so that the first and the second AFMpinning layers have different AFM pinning temperatures.
 5. The TTM ofclaim 1, further comprising: the first AFM pinning layer being formed ofa first thickness; and the second AFM pinning layer being formed of asecond thickness different from the first thickness, so that the firstand the second AFM pinning layers have different AFM pinningtemperatures.
 6. The TTM of claim 1, wherein the base region consists ofthe free layer structure.
 7. A magnetic head, comprising; a read sensorcomprising a three terminal magnetic sensor (TTM); the TTM having: asensor stack structure comprising a base region, a collector region, andan emitter region; a first barrier layer located between the emitterregion and the base region; a second barrier layer located between thecollector region and the base region; a plurality of terminals of theTTM comprising a base lead coupled to the base region, a collector leadcoupled to the collector region, and an emitter lead coupled to theemitter region; the collector region comprising a layer of semiconductormaterial; the base region being made of ferromagnetic materials andcomprising a free layer structure; one of the emitter region and thecollector region comprising a pinned layer structure; the other one ofthe emitter region and the collector region comprising an in-stacklongitudinal biasing layer structure; the in-stack longitudinal biasinglayer structure comprising a first ferromagnetic (FM) pinned layer and afirst antiferromagnetic (AFM) pinning layer which magnetically pins thefirst FM pinned layer; the in-stack longitudinal biasing layer structurebeing formed in stack with the sensor stack structure and having amagnetic moment that is parallel to a sensing plane of the TTM forlongitudinally biasing the free layer structure; the pinned layerstructure including a second FM pinned layer and a second AFM pinninglayer which magnetically pins the second FM pinned layer; an insulatorlayer which is offset from the sensing plane and in between the baseregion and the collector region; and a layer of metal which is offsetfrom the sensing plane and in contact with the ferromagnetic materialsof the base region, the layer of metal having an electrical resistivityof less than 10 uΩ-centimeters so that a combined electrical resistivityof the base region is between about 2-18 uΩ-centimeters.
 8. The magnetichead of claim 7, wherein one of the barrier layers serves as anon-magnetic spacer layer between the free layer structure and thein-stack longitudinal biasing layer structure.
 9. The magnetic head ofclaim 7, wherein one of the barrier layers serves as a non-magneticspacer layer between the free layer structure and the pinned layerstructure.
 10. The magnetic head of claim 7, further comprising: thefirst AFM pinning layer being formed of a first material; and the secondAFM pinning layer being formed of a second material that is not presentin the first AFM pinning layer, so that the first and the second AFMpinning layers have different AFM pinning temperatures.
 11. The magnetichead of claim 7, further comprising: the first AFM pinning layer beingformed of a first thickness; and the second AFM pinning layer beingformed of a second thickness different from the first thickness, so thatthe first and the second AFM pinning layers have different AFM pinningtemperatures.
 12. The magnetic head of claim 10, wherein the firstmaterial comprises one of PtMn and IrMn, and the second materialcomprises the other of PtMn and IrMn.
 13. The magnetic head of claim 7,wherein the base region consists of the free layer structure.
 14. A diskdrive, comprising: a slider; a magnetic head carried on the slider; awrite head portion of the magnetic head; a read head portion of themagnetic head; the read head portion including a three terminal magneticsensor (TTM); the TTM having: a sensor stack structure comprising a baseregion, a collector region, and an emitter region; a first barrier layerlocated between the emitter region and the base region; a second barrierlayer located between the collector region and the base region; aplurality of terminals of the TTM comprising a base lead coupled to thebase region, a collector lead coupled to the collector region, and anemitter lead coupled to the emitter region; the collector regioncomprising a layer of semiconductor material; the base region being madeof ferromagnetic materials and comprising a free layer structure; one ofthe emitter region and the collector region comprising a pinned layerstructure; the other one of the emitter region and the collector regioncomprising an in-stack longitudinal biasing layer structure; thein-stack longitudinal biasing layer structure comprising a firstferromagnetic (FM) pinned layer and a first antiferromagnetic (AFM)pinning layer which magnetically pins the first FM pinned layer; thein-stack longitudinal biasing layer structure being formed in stack withthe sensor stack structure and having a magnetic moment that is parallelto a sensing plane of the TTM for longitudinally biasing the free layerstructure; the pinned layer structure including a second FM pinned layerand a second AFM pinning layer which magnetically pins the second FMpinned layer; an insulator layer which is offset from the sensing planeand in between the base region and the collector region; and a layer ofmetal which is offset from the sensing plane and in contact with theferromagnetic materials of the base region, the layer of metal having anelectrical resistivity of less than 10 uΩ-centimeters so that a combinedelectrical resistivity of the base region is between about 2-18uΩ-centimeters.
 15. The disk drive of claim 14, wherein one of thebarrier layers serves as a non-magnetic spacer layer between the freelayer structure and the in-stack longitudinal biasing layer structure.16. The disk drive of claim 14, wherein one of the barrier layers servesas a non-magnetic spacer layer between the free layer structure and thepinned layer structure.
 17. The disk drive of claim 14, furthercomprising: the first AFM pinning layer being formed of a firstmaterial; and the second AFM pinning layer being formed of a secondmaterial that is not present in the first AFM pinning layer, so that thefirst and the second AFM pinning layers have different AFM pinningtemperatures.
 18. The disk drive of claim 14, further comprising: thefirst AFM pinning layer being formed of a first thickness; and thesecond AFM pinning layer being formed of a second thickness differentfrom the first thickness, so that the first and the second AFM pinninglayers have different AFM pinning temperatures.
 19. The disk drive ofclaim 17, wherein the first material comprises one of PtMn and IrMn, andthe second material comprises the other of PtMn and IrMn.